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U. S. P. R. R. EXP. AND SURVEYS-ZOOLOGY-GENERAL REPORT. 
scarcely reach to the bases of the claws of the digits next them ; in N. micropus, the claw of the 
second finger reaches nearly to the middle of the third. The toes are similarly circumstanced. 
In N. floridana, the first claw reaches to the penultimate articulation of the second toe ; the fifth 
claw to the base of the fourth. In N. micropus, the outer toes are longer and the inner shorter 
than in the other species. The color of N. micropus, even in adult specimens, is much darker 
and more plumbeous, with less mixture of yellowish brown on the sides. The white on the feet 
and legs is more restricted. 
Compared with N. floridana, the skull of this species is much broader between the zygomata, 
in this respect approaching to N. occidentals ; the divergence, too, of these hones behind is 
greater. The nose is longer. The concave depression in the top of the head between the orbits 
is deeper ; the posterior wall of the orbit more vertical, and nearer to a perpendicular with the 
axis of the head. The orbital opening is wider. There is a firmly attached rudimentary 
lachrymal hone which I have not obtained in other species. The outline of the head above is 
gently convex, as in other thin-tailed species. The temporal ridges are more distinct than in 
N. floridana. The molars are broader and the angles more rounded ; in fact, larger every way. 
The outlines of the lower jaw, too, are different. The neck of the condyloid process is longer ; 
its axis more horizontal ; the articulating surface is larger and more below the level of the 
coronoid process ; the bottom of the notch between the two more horizontal; the notch below 
the condyloid deeper ; the entire ramus lower, and the body of the hone anterior to the molars 
deeper. The incisors, upper and lower, are wider and larger. 
The dark colors of this species, although resembling somewhat those of the immature Florida 
rat, and of many young rodents generally, appear to he permanent, as the specimens examined 
appear perfectly adult, eren larger than the Florida rat. The shade, too, is quite different from 
the immature tints above mentioned, in being more lustrous, and more like the colors of the 
black rat. An additional confirmation of the idea that the species does not become lighter, is 
found in the MS. description by Doctor Berlandier, who was very familiar with it, and who 
mentions it as “ grayish ash on the sides, darker on the hack ; throat, breast, belly, feet, and 
hands whitish.” 
A very striking difference between the skulls of N. micropus and floridana is seen in the 
shape of the posterior outline of the bony palate. This, in the former, has the outline of the 
notched part narrow, wedge-shaped, truncate anteriorly, and scarcely reaching beyond the 
middle of the posterior molar. Between the last molar and the side of the notch is a width of 
hone of the diameter of the molar itself, the greatest width of the notch not being more than 
twice this strip of hone. In N. floridana, the notch extends as far as the middle molar, and 
involves nearly the entire space between the posterior molars on either side. N. mexicana 
differs from floridana in the same character, except that the notch extends further forward than 
in N. micropus. In fact, all the slender-tailed species from the west agree in the narrow notch, 
as described. 
The skull of N. fuscipes exhibits, in a marked degree, the peculiarity of the western Neotomas, 
in reference to the notch of the palate. This is very narrow ; the sides parallel, the anterior 
end transverse, the notch being thus exactly rectangular, and only about .08 of an inch wide 
at any part; about the width of the molars, or one-fifth the distance between the outer edges of 
the two rows of the latter. 
